Wire mergedTracerTags as a read-through parent at span build (level-split phase 1)#11932
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Wire mergedTracerTags as a read-through parent at span build (level-split phase 1)#11932dougqh wants to merge 4 commits into
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Version is conditionally managed by InternalTagsAdder (added only when service == DD_SERVICE and not set during the request). It was being applied to every span via the trace-level bundle, then immediately stripped by a per-span removeTag(VERSION) — apply-then-remove, net zero. Exclude it from the bundle once at config build (withTracerTags) instead. This is behavior-preserving today, and it prepares the bundle to become a read-through parent: a removeTag on a key that lived in the parent would mint a per-span tombstone. With version excluded, the retained per-span removeTag(VERSION) (which still wipes a builder-set version, preserving the existing semantics) is a cheap local op, never a tombstone. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Level-split phase 1: when the trace-level bundle has no interceptable tags (!mergedTracerTagsNeedsIntercept), attach it as a read-through parent of the span's tags (shared by reference) instead of copying its entries into every span. When it does need interception, fall back to the copy path (the interceptor's per-span side-effects can't be shared). - TagMap.withParent promoted to the interface (was package-private on OptimizedTagMap) — the public wiring deferred from the mechanism change. - DDSpanContext.parentTags attaches the (frozen) parent to unsafeTags. - CoreTracer span-build gates copy-vs-share on needsIntercept. mergedTracerTags is the precedence floor (overridden by all other contributors), so attaching it as the lowest-precedence parent preserves ordering. Version was already excluded from the bundle, so the per-span removeTag never tombstones. Tag-touching tests (CoreSpanBuilder/CoreTracer/DDSpan/InternalTagsAdder) green. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Models span-build tag assembly: copyDown (putAll the frozen trace-level bundle
into a fresh span map, then span tags) vs readThrough (attach the bundle as a
read-through parent, span tags local only). Run with -prof gc to isolate the
per-span allocation read-through saves. Swept by traceTagCount {3,7,15} so the
win can be seen scaling with the bundle size; 7 ~ a realistic mergedTracerTags.
Quick read (noisy box): readThrough ~38% less alloc (deterministic) and ~1.7x
throughput. The alloc delta is bucket structure (BucketGroup clones + fewer local
collisions), not Entry objects -- putAll-into-empty already shares frozen entries.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Rework the wiring onto the footgun-free API: instead of the post-construction DDSpanContext.parentTags()/withParent() seam, thread a nullable read-through parent into the DDSpanContext constructor and build unsafeTags via TagMap.createFromParent(parent) when present. CoreTracer passes mergedTracerTags on the !needsIntercept path (null otherwise), so the parent is fixed at construction and read-through relies on a guarantee, not an unenforced convention. Removes parentTags(); a back-compat 24-arg ctor delegates with a null parent so existing callers are unaffected. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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Stacked on #11789 (TagMap read-through mechanism) — review that first.
Level-split phase 1: the wiring. Attaches
mergedTracerTagsas a read-through parent at span build (gated on!mergedTracerTagsNeedsIntercept) instead of copying it into every span's storage. This is the change that actually activates read-through — #11789 alone is inert (parent == null).Commits: config-version handling out of the trace-level bundle, the read-through flip (
DDSpanContext.parentTags/CoreTracercopy-vs-share gate), and aTagMapReadThroughBenchmark.Draft — description to be refined; posting now so review can start this week ahead of the release cut.
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